The present invention relates to a felt for papermaking machines and more particularly to a multi-layer felt for use in the wet press section of a papermaking machine.
A number of attempts have been made to provide a construction particularly suitable for use in the wet press section of a papermaking machine. In the construction of a wet press felt, the desirability of maintaining a controlled void volume within the felt is recognized. In use, loss of void volume due to compaction of a wet press felt upon repeated passes through the nip of wet press rollers is common. The compaction of the wet press felt shortens the life of the felt by limiting the drainage of water through the felt. This also reduces the efficiency of the papermaking machine. As papermaking machines have developed, machine felt speeds of between 4000 and 5000 feet per minute have become common. Due to such high speeds, the resulting forces on the felt can also shorten the life of the felt if the felt is not sufficiently resistant to such loads.
Typical prior art wet press felts have included a woven fabric base to which is affixed a batt material. See, for example, the description given in U.S. Pat. Nos. 4,520,059; 4,503,113; 4,482,601, 4,461,803, 4,425,392; 4,356,225; 4,187,618; and 3,772,746.
Wet press felts which include support or filling material within the batt layers are known. For example, U.S. Pat. No. 4,357,386 discloses a composite papermaker's felt made up of a woven textile base layer, an intermediate layer of polymeric resin foam and a covering layer of non-woven batt material. U.S. Pat. No. 4,500,588 discloses a felt for papermaking which includes a woven support fabric and a non-woven fiber batt layer needled to the support fabric which includes a resinous or elastomeric air permeable filling within the layer of batt material. U.S. Pat. No. 4,427,734 discloses a wet press felt which includes a woven fabric base having layers of non-woven batt material needled thereto in which layers of synthetic textile fiber mesh are interposed between adjacent layers of the batt material.
Canadian Patent No. 691,463 discloses a papermaker's felt which comprises an open mesh woven fabric base having layers of felt or fiber material needled to both sides. The felt layer optionally includes meltable or shrinkable fiber dispersed within the felt layer so that upon heating, interconnection of the layers is increased. U.S. Pat. Nos. 4,528,236 and 4,579,771 disclose a papermaker's fabric which include a base of intermeshed monofilament spiral coils and an upper layer of batt material. The batt layer is adhered to the base by a layer of adhesive applied to the interface or by dispersing meltable fibers throughout the batt layer so that upon heating, the batt layer adheres to the base.